Foam fractionation is a chemical process in which hydrophobic molecules are preferentially separated from a liquid solution using rising columns of foam. In general two mechanisms provide for effective removal of molecules from a solution, first a target molecule adsorbs to a bubble surface, and then the bubbles form a foam which travels up a column and is discharged to the foamate stream of foam fractionation.
Foam fractionation predominantly removes surfactant contaminant molecules (molecules that have polar and non-polar ends). At the air-water interface of the bubbles the surfactant molecules orientate themselves so that the non-polar hydrophobic end of the surfactant molecules is in air and the polar hydrophilic end of the molecule is in water. As the bubbles rise to the top of the fractionating column they remove the contaminants and settle at the top of the column as a foam.
Many organic substances can be removed by foam fractionation and larger biological material, such as algae, bacteria and viruses can also be removed. Particles present in the water can also be removed. It is thought that biological material and particles become trapped in the film surrounding the air bubbles. Inorganic material can also be removed if it can form some kind of a bond with organic matter in the water. For example, calcium carbonate and calcium phosphate complexes can collect organic matter in the water forming micro-flocs that can get trapped in the film surrounding the air bubbles. Metal ions can also form ligands with organic molecules, and glycoproteins have a high affinity for trace metals and therefore facilitate removal of metal ion species from water. Foam fractionation to date has encountered many difficulties when used in removing particles from an oil/aqueous mixed phase.
Efficient contaminant removal is complex and depends on many factors including air to water ratio; column height; air bubble diameter; air/water contact time; air bubble flow rate; foaming agent: foam wetness; downward water flow rate; foam stability; and collision speed between the water and the rising gas. Foam stability is also be an important factor and can be defined as the resistance to contaminant drainage from the foam, without foam rupturing. The foam must be stable enough to be removed from the fractionating column, without leaching of the contaminant molecules into the water occurring. The most widely used foaming agent cocamide DEA, or cocamide diethanolamine, has come under regulatory pressure and the International Agency for Research on Cancer (IARC) lists coconut oil diethanolamine condensate (cocamide DEA) as an IARC Group 2B carcinogen, which identifies this chemical as possibly carcinogenic to humans.
The use of surfactants, such as soap and synthetic detergents, for dissolving organic compounds, is well known in the art. Particularly, surfactant is applied to hydrophobic organic compounds (chemical substances which have a very low solubility in water) for the purpose either dissolving, emulsifying or dispersing the organic compounds in a water environment. Another particular property of surfactant molecules which may be related to solubilization is aggregation to sub-micron droplets, referred to in the art as micelles. In a water environment, the surfactant molecules constituting the micelle are oriented with the hydrophilic heads towards the water, i.e., outwards, and the hydrophobic tails towards the interior of the micelle. Consequently, the micelle's interior is a hydrophobic micro-environment, capable of retaining organic solutes.
It is also well known to separate surfactant micelles from water by means of an ultrafiltration mechanism. Foam fractionation may also be used. According to this mechanism, liquids containing surfactants may be purified by passing a gas through the liquid, thereby generating a foam. The foam is collected and condensed by means of a mechanical foam breaker. The method is suitable for purifying dilute surfactant solutions, since the concentration of surfactant in the foam is higher than in the original liquid.
Accordingly it is an object herein to provide a foam fractionation method that does not employ the use of cocamide DEA.
It is yet another object of the invention to provide a composition employing a surfactant platform that can be used with foam fractionation to remove multiply charged cations and total suspended solids dissolved in the same.
Other objects, aspects and advantages of this invention will be apparent to one skilled in the art in view of the following disclosure, the drawings, and the appended claims.